The Dark Palazzo — Virginia Coffman

When lovely young Rachel Carewe arrives in Venice seeking her father, the British ambassador, she is shocked by his strangely altered appearance. She is also disturbed by the fanatic hold his housekeeper Mira has over him.

It becomes obvious soon enough that they are lovers. What is not obvious is why Mira should nourish such hatred for Rachel, or why Rachel suddenly should find her life in danger. Apparently there is something Rachel knows -- something that is a secret even from herself. And that knowledge has become her death warrant.